A delta-sigma modulator generally suffers a quantization noise and a digital-to-analog converter (DAC) noise that may worsen the signal quality and circuit efficiency. The quantization noise can be reduced by increasing an over-sampling ratio (OSR), quantization bit number or loop filter order. However, the DAC noise from a bias source cannot be easily cancelled while a large swing input is applied. One solution to cancel the DAC noise is to add a bulky resistor-capacitor low-pass filter in the bias path. However, the bulky resistor-capacitor low-pass filter may occupy large chip area and increase the manufacturing cost.